(All about potentiometry) Potentiometry, Reference Electrode, Indicator Electrode, Ion Selective Electrode, Potentiometric titration, Application, Advantages, Disadvantages etc.

1. POTENTIOMETRY
Presented By :
Md. Chand
MSc. PC (2021-2023)
Jiwaji University Gwalior, Gwalior, MP (474011)
Jiwaji University
Submitted to :
Dr. Nimisha Jadon
(Asst. Prof.)

2. Introduction :-
Potentiometry is a branch of electrochemistry which
deals with the study and measurement of electrode
potential, measuring the potential or EMF of a solution
by using the set of indicator electrode & reference
electrode.

3. Principle :-
The Principle involved in the potentiometry is when
the pair of electrodes is placed in the sample solution
it shows the potential difference by the addition of the
titrant or by the change in the concentration of the
ions.

4. Theory :-
The main theory involved in the potentiometry is when the
known potential electrode immersed in the sample solution
then the potential is given by ‘Nernst Equation’.
E = E⁰+(0.592/n)Log C
Where; E⁰ = Std. Potential Of The Electrode.
n = Valency of ions.
C = Concentration of ions.

5. Potentiometry Instrumentation :-

6. Reference Electrode :-
The reference electrode is the
electrode which contains of it’s own
potential value and it is stable when
dipped into sample solution. The ‘Salt
Bridge’ is used to prevent the
interference of the analyte solution
with that of reference solution.

7. Types of Reference Electrode :-
1. Standard Hydrogen Electrode.
2. Saturated Calomel Reference Electrode.
3. Silver-Silver Chloride Refrence Electrode.
1. Std. Hydrogen Electrode :-
Hydrogen Electrodes were widely
used in early electrochemical studies
not only as reference electrodes but
also as indicator electrodes for
determining pH.
The composition of this type of
electrode can be represented as
below.
Pt., H2 (p atm) | H+ (aH+ = x).

8. Advantages and Disadvantage of
Hydrogen Electrode :-
Advantages :-
(i) It can be used over the entire pH.
(ii) It can be used as a reference electrode when dipped with standard acid solution and as
an indicator electrode when dipped into a sample solution.
(iii) It is the primary reference standard against which the potential of other electrodes are
measured.
Disadvantages :-
(i) It is affected by the presence of oxidising agent and reducing agent.
(ii) It is rather difficult to regulate the pressure of H2 gas to be exactly 1 atm
throughout the experiment.
(iii) Platinum foil gets easily poisoned by the impurities present in the H2 gas and HCL
solution.

9. 2. Saturated Calomel Electrode :-
Calomel reference electrode of 'Mercury’ is contact with a solution that is saturated
with mercury chloride (calomel) and that also contains a known concentration of
potassium chloride (KCl) calomel half cells can be represented as follows.
Hg|Hg2Cl2 (Saturated), KCl (xM)||
Where; x = Molar Concentration of KCl in the solution.
The electrode potential for this half-cell is
determined by the reaction below.
Hg2Cl2 (S) + 2e ↔️ 2Hg (L) 2Cl- (Aq).
• Potential of the electrode depends on the
concentration of the KCl solution and temperature.
• Tip is filled with crystals of KCl and Porous ping of
asbestors.

10. 3. Silver-Silver Chloride Electrode :-
It is also widely used reference electrode
because, It is 'Simple’
‘Inexpensive’
‘Very Stable’
'Non-Toxic’
It is mainly used with saturated KCl electrode (KCl
electrolyte) but can be used with low concentration such as
1M KCl and even directly in sea water.
Silver (Ag) wire coated electrolytically with AgCl2 and
dipped into KCl .
Potential depends on the concentration of the KCl and
temperature
Ag|AgCl (Saturated), Kcl (Saturated)||
AgCl (S) +e↔️Ag (S) + Cl- (Aq).
E⁰ = 0.199V
Advantage :-
Easy to use
Disadvantage :-
Difficult to prepare

11. * Indicator Electrode :-
It is used to measure the potential of analyte solution comparing
with that of reference electrode, It’s potential is directly proportional
to the ions concentration.
Example :-
(i). Hydrogen electrode.
(ii). Glass electrode.
Types Of Indicator Electrodes :-
1. Glass Indicator Electrode.
2. Metal/Metallic IE.
3. Ion Selective Electrode (ISE)
or Specific Ion Selective (SIE).

12. 1. Glass Indicator Electrode :-
It is mainly used to determine the pH of the sample concentration.
The glass electrode is dipped into the sample solution as we know
the glass acts as semipermeable, it means it allows to pass/transfer
H+ ions from sample solution to glass electrode cation in glass
exchange with H+ from solution.
H+ + Na+ Cl- ↔️ Na+ + H+ Cl-
Soln. Glass Soln. Glass.
According to this reaction the H+ ion in the solution which attracts
with the Cl- ion of the glass which form H+ or Cl- that is HCl.

13. 2. Metal/Metallic IE :-
Metallic electrodes which are subject of this section,
the potential of a metallic electrode is determined by
the position of the redox reaction at the electrode
solution interface.
Construction :-
Electrode is made up of the sample solution.
Disadvantage :-
• Never used in acidic solution.
• Only used in neutral and basidic solution.
• Less sensitive electrode.

14. 3. Ion-Selective Electrode ISE
or Specific ion electrode SIE :-
Ion-Selective Electrodes (ISE) are also known as Specific Ion
Electrode (SIE), is a sensor that converts the activity of a specific
ion dissolved in a solution into an electrical potential, which can be
measured by a voltmeter or pH meter, and not affected by other
ions because here we used ion selective membrane.
Potential :-
The voltage is theoretically dependent on the negative
logarithm of the ionic activity, according to the 'Nernst
Equation’.
Uses :-
ISE are used in analytical chemistry, bio-chemical/biophysical
research.
Where; measurements of ionic concentration in aqueous solutions
are required.

15. Advantages of ISE :-
 Easy to operate.
 It has resistance to the solvent.
 Resistance to chemical attacks.
 Wide range of concentration can be measured.
 It is used in biological & medical applications.
 It can also used in Colour and turbid solution.
 It can be monitor the change of activity of ions with time.
 It can be measure or sense the cation as well as anion.
Types of ISE :-
1. Glass Membrane ISE.
2. Solid state or crystalline ISE.
3. Gas Sensing ISE.
4. Liquid Membrane ISE.
5. Enzyme Based ISE.

16. 1. Glass Membrane ISE :-
In this membrane electrode the membrane is permeable to
only univalent cation (H+, Na+)
• Glass membrane manufactured from SiO2 with negatively
charged oxygen atom.
• Inside the glass bulb, a dilute HCl solution and silver wire
coated with a layer of silver chloride.
• The electrode is immersed in the solution and pH is
measured.
Example :-
pH Electrode.
Properties of Gass pH electrode :-
• Potential not affected by the presence of oxidising or
reducing agents.
• Operates over a wide pH range.
•Fast response.
• Very selective.
• Long lifespan.

17. 2. Solid State or Crystalline ISE :-
Solid state electrodes are selective primarily to anions, it
may be a homogeneous/heterogeneous membrane
electrode.
Homogeneous Membrane Electrode :- Ion selective
electrodes in which the membrane is a crystalline material
(Ag/Ag2S).
Heterogeneous Membrane Electrode :- Ion selective
electrodes prepared of an active substance or mixture of
active substance (Silicon rubber or PVC).
•Usually ionic compound.
•Crushed powder, metal and formed.
• Sometimes doped to increase conductivity.
• Operation similar to glass membrane.

18. 3. Gas Sensing ISE :-
An electrode in which a gas permeable membrane separates
the test solution fluid from an aqueous electrode solution in
contact with an ion selective electrode.
• A galvanic cell which potential is related to the
concentration of a gas in solution.
• A thin gas permeable membrane (PTFE) serves as a barrier
between internal and analyte solutions.
• Allow small gas molecules to pass and dissolve into internal
solution.

19. 4. Liquid Membrane ISE :-
Liquid membrane is a type of ISE based on water
immiscible liquid substances produced in a
polymeric membrane used for direct
potentiometric measurements, used for direct
measurement of several polyvalent cations
(cation) as well as a certain anions, and potential
develops across the interface between the analyte
solution and a liquid ion exchange (that bond
with analyte).

20. 5. Enzyme Based or Biochemical ISE :-
Enzyme electrodes are based on the principle that an
enzyme reacts with a specific substance and the product of
this reaction is detected by ISE, enzyme is immobilize at the
surface of electrode, it is not a true ISE but usually
considered within the ion specific electrode.
Applications of Ion-Selective
Electrodes :-
• It is used in cosmetics & pharmaceuticals industries.
• It is used in monitoring of soil water & air pollutants.
• It is used to determine the activity of ions & sensors in titration.
• As it works on colour & turbid solution, it is applicable in the
quality detection.

21. * Direct Potentiometry
A rapid & convenient method to determine the activity of
cations/anions, the technique used in this method is a
comparison of the potential developed by the indicator
electrode, when it is immersed in in the solution with that
standard solution of the analyte.
Potentiometric probes used in direct potentiometry are
attractive sensing tool, they give information on ion activities
which is after uniquely useful.
Potentiometric Measurements :-
1. Calibration Method.
2. Standard Addition Method.
1. ➡️
2. ➡️

22. * Potentiometric Titration :-
The measurement of potential E or pH against volume of titrant or detection
of end point of titration by change in potential of analyte is called
potentiometric titration.
This method is also known as indirect potentiometry, potentiometric
titrations are the most accurate method because the potential follows the
actual change in activity and therefore end point will concide directly with
the equivalence point (end point). Provide more reliable data than the usual
titration method useful with coloured/turbid solutions.
When potentiometric titration is used?
It is used when the end points are very difficult to determine
either when;
° Very diluted solution.
° Coloured and turbid solution.
° Absence of a suitable indicator.

23. Instruments Used :-
 pH meter.
 Reference electrode.
 Indicator electrode.
 Voltmeter which measures the potential difference.
 Magnetic stirrer.
 Hot plate (use the stirrer and make sure heat is off).
 Magnet capsule.
 Glass (Burrete and beaker).
Applications of Potentiometry :-
1. Direct potentiometry.
2. Environmental chemistry.
3. Agriculture.
4. Food processings.
5. Agriculture.
6. Fluorine in drinking water and other drinkers.
7. Salt content of meat, fish, dairy products, fruits, juice brewing solutions.
8. Potentiometric Titrations.

24. (i). Acid-Base Titration.
(ii). Redox Titration.
(iii). Precipitation Titration.
(iv). Complexometric Titration.
(i). Acid-Base Titration :-
Titration can be done in aqueous and non-aqueous medium.
E+K-0.0592pH.
Aqueous Medium :- Any strength – 0.01N, 0.1N, 1N.
Acid-Base combinations;
• Weak Acid – Weak Base. • Weak Acid – Strong Base.
(Ch3CooH vs NH4OH). (CH3CooH – NaOH).
•Strong Acid – Strong Base. • Strong Acid – Weak Base.
(HCl – NaOH). (HCl – NH4OH).
• Mixture of acids vs bases : (CH3CooH+HCl) vs NaOH.
• Mixture of bases vs acids : (NH4OH+NAOH) vs HCl.
• Poly basis acids vs bases : Citric acid vs NAOH.
Tartaric acid vs NAOH

25. Non-Aqueous medium :-
• Weak acid vs potassium (KOME) Lithium methoxide (Liome).
Ex.= Barbituric acid vs Liome.
• Weak Bases vs Perchloric acid.
Ex.= Ephedrine hydrochloride.
• Indicator Electrode : Glass electrode.
• Reference electrode : SCE.
* End Point ➡️ The end point of the
acid/base titration curve is called inflaction
point.

26. 2. Redox Titration :-
• Reaction : - Fe2+ Ce3+ +Fe3+.
• Ce4+ is an oxidising agent which oxidises Fe2+ (Ferrous) to Fe3+ (Ferric ion), in this
process. Ce4+ (Cerric) gels reduced to Ce3+ (Cerrous ions).
• E = E⁰+0.0592/n x log (ox)/(red).
• Where; E⁰ = Standard potential.
n = No. of electrons involved in the reaction.
(ox) = Concentration of Oxidant.
(red) = Concentration of reductant.
• Reference Electrod : SCE, Ag-AgCl2 electrode.
• Indicator Electrode : Platinum wire or foil.
Mv scale is used for end point detection.
Ex = Ferrous Ammonium Sulphate in dilute.
H2So4 vs KMNo4/K2Cr2O7.

27. 3. Precipitation Titration :-
• For quantitative determination of several ions or elements precipitating agents are
used as titrants.
• End point is determined by potentiometric method.
• E⁰ = E⁰+0.0592/n x log [Mn+].
Where; [Mn+] = Concentration of ions.
n = electronic state.
• Reference Electrode : SCE, H2, Ag-AgCl2 electrode.
• Indicator Electrode : Silver wire electrode.
Ex = Determination of Hg, Ag, Pb, Cu and other ions using precipitants to form
insoluble salts.

28. 4. Complexometric Titration :-
• Metallic ion (Divalent) can be titrated against disodium esdetate solutions
by potentiometric method.
• Measurements are made in mv scale.
• Reference Electrode : SCE/any other.
• Hg Electrode.
Ex = Di and Trivalent ions.
(Mix of Bi3+, Cd2+, Ca2+ by using EDTA)
Applications of Potentiometric Titration :-
(i). Acid-Base Titration :- It is used to determine the pH of different solutions.
(ii). Precipitation Titration :- By this titration we can determine the presence of hallogens in the
sample.
(iii). Complexometric Titration :- By this titration we can determine the cations like Bi³+, Cd²+,
Ca+, Mg²+, etc in its cationic mixture.